Subsea electronics modules are preferably used in subsea control units (SCU), e.g., wellhead control units (WCU), for exploring and exploiting gas and oil fields located at the seabed. Gas and oil fields that are explored or exploited using electronic communication to the wellheads or to other subsea control units are sometimes called “electronic fields” (e-fields).
Typically, several subsea control units and several sensors are located in a vicinity of a respective gas or oil field, and are connected to a topside control site. For this purpose, subsea communication is used. For example, process data are transmitted between the topside control site and the subsea control units. In order not to require individual communication and power lines for each subsea control unit, the subsea control units are arranged on the seabed in a network topology. One network member is equipped with a modem for subsea communication with the topside control site. The process data are routed within the network to reach the respective recipient, e.g. either the topside control site or a certain subsea electronic module. Usually, a differential serial bus is used for the network.
In prior art, different techniques for subsea communication have been described. On the one hand, there are wired electric or optical connections, on the other hand there are wireless connections. The wired connections can be subdivided into a first group providing communication lines for electronic or optical connections separate from electric power lines, and a second group utilising power lines for electronic communications. In the latter case, advantageously no separate communication lines are needed.
Known subsea control units require at least two input/output (I/O) interface cards for acquisition and/or output of digital and analogue process data. In addition, the known subsea control units require one routing card for each network/bus member that is to be directly connected to them. Hence, if several Slave subsea control units are to be connected to one subsea Master control unit comprising a modem, the same number of routing cards has to be installed into the subsea Master control unit. The number of required cards increases if process data is to be acquired or if a process has to be controlled. These multiple cards are space-consuming and power-consuming.